American Trapezoidal Thread (ACME)

There are two types of trapezoidal thread specifications, namely American trapezoidal thread (ACME, also known as ACME thread) with an Asan angle of 29°, and 30° Metric trapezoidal thread. Although the transmission efficiency of trapezoidal threads is lower than that of square threads, because square threads are not easy to process and manufacture, trapezoidal threads are generally used for transmission screws.

In the American ASME/ANSI B1.5 standard, the universal dimensions of ACME trapezoidal threads are defined, which are divided into 2G, 3G, and 4G according to the clearance tolerance of internal and external threads. Grade, it is recommended that the internal and external threads adopt the same tolerance grade. Generally, 2G is preferred. If less clearance is required, 3G or 4G is used.

Thread representation

[Name diameter] - [Number of teeth per inch] ACME

Example

¼ - 16 ACME

Thread Specifications

Thread Angle: 29° (American ACME)
Standard: ASME/ANSI B1.5
Tolerance Grades: 2G, 3G, 4G
Application: Power transmission screws

ACME Thread Specifications

Unit: mm

Name of Thread	Threads per Inch	Pitch P	Major Diameter D, d	Median Diameter D₂, d₂	Minor Diameter D₁, d₁

FAQ

What is the difference between ACME and metric trapezoidal threads?
ACME threads have a 29° thread angle and follow ASME/ANSI B1.5 standards, while metric trapezoidal threads have a 30° angle and follow ISO standards. ACME threads are measured in inches with threads per inch (TPI), while metric threads use millimeter pitch.
Why are trapezoidal threads preferred over square threads for power transmission?
Although square threads have higher transmission efficiency, trapezoidal threads are easier to manufacture and machine. They provide better strength, easier assembly/disassembly, and standardized dimensions. The slight efficiency loss is offset by manufacturing advantages and reliability.
What do the tolerance grades 2G, 3G, and 4G mean for ACME threads?
These grades indicate the clearance tolerance between internal and external threads. 2G is the preferred general-purpose grade with moderate clearance. 3G provides tighter clearance for more precise applications. 4G offers the tightest clearance for high-precision power transmission applications.
How do I read ACME thread designations like "¼-16 ACME"?
The first number (¼) is the major diameter in inches, the second number (16) is the threads per inch (TPI), and "ACME" identifies the thread type. This designation tells you the thread size and pitch in the American system.
What are typical applications for ACME threads?
ACME threads are commonly used in lead screws, jack screws, vise screws, lathe feed screws, and other power transmission applications. They're ideal for converting rotary motion to linear motion with good mechanical advantage and reasonable efficiency.
Can ACME threads be used with metric components?
ACME threads are not directly compatible with metric trapezoidal threads due to different angles (29° vs 30°) and measurement systems. However, adapters or custom components can be designed to interface between ACME and metric systems when necessary.